1. Field of the Invention
This invention relates to a novel composition of matter and to its use as an inhibitor for light-induced yellowing in organic compounds. More particularly, this invention relates to alkylthio alkyl phthalates and their usefulness as inhibitors in preventing yellowing of polymeric materials as a result of contact with aromatic amines.
2. Description of the Prior Art
It is well recognized that oxygen in combination with visible or ultraviolet light causes serious degradation in a variety of organic materials. The speed of such degradation is dependent on a variety of factors, such as the type of organic material being acted upon, as well as the conditions of exposure to oxygen, light, and heat. It is known that these adverse effects can be greatly retarded by the use of antioxidants, e.g. substances that inhibit or retard reactions promoted by oxygen and/or peroxides. These antioxidants are believed to act as free-radical inhibitors, effectively tying up any light or oxygen-produced free radicals, thereby preventing such free radicals from chain or disproportionation reactions which produce color-forming bodies. Those antioxidants most widely used to inhibit such oxidative color formation are selected from the aromatic amines. The most popular of such antioxidants are the diphenyl amines, the phenylene diamines, the alkylene diamines, and the naphthyl amines. These compounds have found extensive use as antioxidants in rubber vulcanizates. However, it is a well-recognized phenomenon that aromatic amines in general are themselves susceptible to light-induced oxidation, although not quite as readily as the substrates in which they may be incorporated. Such oxidation normally results in the formation of colored bodies. When the aforementioned antioxidants are used in rubber vulcanizates, such are conventionally highly filled with carbon black, and color resulting from the presence of such amine oxidative products does not pose any particular problem. However, these antioxidants can impart to polymeric floor coverings and the like an oxidative color as a result of contact of materials containing them, e.g. from rubber sole-generated heel marks, rubber padding, and the like. Such color normally appears as a yellow stain diffused deeply into the polymeric wear layer that is impossible to remove without unsightly distortion or even destruction of the wear layer. This yellowing has commonly been referred to as traffic staining and is a significant problem in commercial flooring materials subject to contact with amine antioxidant-containing materials such as rubber vulcanizates.